How to decrypt encrypted data after reinstall windows

Hello. While you reinstalled Windows and still kept your files, there is a chance the virus is still present on your computer. Therefore, before you do anything, perform a full system scan using a comprehensive anti-malware software. Once you are sure that the virus is eliminated, you can perform several actions to attempt data recovery.
Depending on the virus you were infected with, there might be a file decryptor that was specifically created for it. For example, Trend Micro's decryptor is used for few wide-spread ransomware data recovery.
Alternatively, you can use third-party party software like Data Recovery Pro.
We hope that helps. If you need more detailed information, it would be useful if you would determine the name of the ransomware infection.